Mercedes-Benz has released details of its first hybrid drive system for a passenger car. It uses a V6 petrol engine and a compact electric motor as well as a space-saving lithium-ion battery. Expect the S 400 BlueHYBRID - as the new model is known - to go on sale in the summer of 2009.
The S 400 BlueHYBRID is based on the S 350, using a development of the 3.5-litre V6 engine. Sandwiched between the motor and the seven-speed automatic transmission in the torque converter housing is a three-phase electric motor. As well as assisting the petrol engine it replaces the starter and alternator. Mercedes has used a lithium-ion battery - a first for a production car - that is compact enough to be packaged under the bonnet.
On the road the 20bhp electric motor provides up to 118lb.ft of torque to help accelerate the S-class from standstill. Combined with the internal combustion engine the total output is 295bhp and 284lb.ft. Under acceleration both power units work together, which is claimed to provide a seamless forward surge. Energy recovery takes place when coasting or braking, where the motor acts as a generator to charge the batteries.
The two stages of electricity generation depend on whether the car is slowing naturally with the throttle closed (but the brakes off) - in which case the generator works at a low level - or when the brakes are applied gently the generator output is increased, which is felt as a stronger braking force. If the driver presses harder on the brake pedal the conventional hydraulic brakes are applied.
Further fuel savings come from the engine stop and start function built into the BlueHYBRID. When coming to a stop from less than 9mph the engine switches off and only restarts when the brake is released or the accelerator pressed. The power steering and air conditioning continue to function when the engine is switched off as they are driven by their own electric motors. Because the hybrid system provides minimal benefit at steady motorway speeds Mercedes has re-engineered the V6 motor to be more efficient with the result that it is slightly more powerful (by about 7bhp) and uses less fuel. The result is a combined cycle fuel consumption of 35.8mpg and carbon dioxide output of 190g/km - the S 350 and even the S 320CDi cannot match the consumption or CO2 figures. Other key performance claims are 0-62mph in 7.2 seconds and a top speed that is limited to 155mph.
The S 400 BlueHYBRID will be produced at Sindelfingen alongside other S-Class models. European sales are expected to start in June 2009 and the hybrid will reach the Chinese market in August and the USA in September 2009. Expect more details of pricing to be announced nearer the launch date.
John Lambert - 18 Sep 2008